help, dome light ground problem

[jc]

need i little help trouble shooting this
heres were im at so far
i have power to the dome light
bulb didnt light
so i grounded it to the cab and it goes on and stays on
no matter what position the headlight switch is in .

this is 67 lwb pu it does not have dome light switches in the door jambs

heres the only thing i can think of-bad headlight switch .
does this sound right to you guys

also are the cluster bulbs available at an auotzone,pepboys or napa
any body know the bulb # i dont thik its the same # as the orginal but i could be wrong

thanks in advance for any insight , JOHN